Electrical telecommunication subscriber lines are often used for both classical narrowband services such as Plain Old Telephone Service (POTS) or Integrated Services Digital Network (ISDN) access, as well as for access to broadband services like Internet access or internet protocol television (IPTV). The broadband access is usually referred to as Digital Subscriber Line (DSL). In order to operate the classical narrowband services and the DSL service simultaneously on the same subscriber line, these two types of service use different frequency ranges on the telecommunication line. A low frequency range is used for the narrowband services, e.g. POTS or ISDN, and a higher frequency range above said low frequency range is used for DSL.
Accordingly, Customer Premises Equipment (CPE) typically includes a splitter to connect terminal equipment or network termination equipment for both the narrowband services and the broadband services to the single telecommunication line. The splitter includes a low-pass filter arranged for preventing high-frequency DSL signals from propagating to terminal or network termination equipment used for the classical narrowband services. The low-pass filter protects the DSL signals against high frequency disturbances that could be caused by terminal and network termination equipment of the narrowband services, in particular by analogue telephones. Furthermore, the low-pass filter prevents DSL signals from propagating to the terminal or network termination equipment for the narrowband services, in particular to an analogue telephone, and thus avoids e.g. audible noise during telephone communications.
It may happen that customers erroneously connect DSL devices, in particular DSL modems, to a connector of the splitter that is intended to be connected with narrowband terminal or network termination equipment (e.g. analogue telephone or ISDN network termination). In case that the narrowband service is POTS, there is the risk that the phone would be connected to a connector of the splitter intended to be connected to the DSL modem (modem connector) while the DSL modem would be connected to a connector of the splitter intended to be connected to the phone. In such a case of erroneous interconnection of the parts of the CPE, the DSL signal, which lies entirely within the stop-band of the low-pass filter of the splitter, would be strongly attenuated when reaching the DSL modem. As a consequence, the performance of the DSL service would be significantly degraded, and in many cases, the DSL modem could not even be able to synchronize with an access node (e.g. a DSL Access Multiplexer, DSLAM) of the network operator.
Known test methods for testing the telecommunication line between the network operator and the subscriber, such as Metallic Line Testing (MELT) or Single Ended Line Test (SELT), generally involved in DSL connectivity troubleshooting, would not show any physical fault on the telecommunication line. Hence, costly and time consuming investigations are often needed to identify the problem.